At Page 0 we prepared a QA type Region which queries APEX_DEBUG_MESSAGES for recent errors.
This is just an idea on how to leverage APEX information for QA purposes.

Note: APEX automatically writes unhandled errors to the Debug log.

Go to Page 0 and remove the Build Option to activate this Region.

Debug can be switched on and off by using either the Developer Toolbar or specifying the Debug Option in the URL.

APEX also offers a PL/SQL API to do the same job: APEX_DEBUG.Enable. See the documentation for details.

With this Application a DB table APEX_CUSTOM_DEBUG_CONTROL is created. You can use such a table to remotely control when and where to activate DEBUG.

To set up the debugging go to Page 99 and define the conditions.

The actual activation code is put in Shared Components -> Security -> PL/SQL Initialization section.

Again, this is just an idea on how to leverage APEX API's.